Electrical apparatus



July 2, 1963 W. o. BROOKS l 3,096,475

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AvTOR/vey W. O. BROOKS ELECTRICAL APPARATUS July 2, 1963 5 Sheets-Sheet 3 Filed May 16, 1958 .PDO 0 D OSLI W/LL/AM o. Baco/ 5 INVENTOR. QLM/M ATTORNEY United States Patent O 3,096,475 ELECTRICAL APPARATUS William 0. Brooks, Los Angeles, Calif., assigner, by mesne assignments, to Thompson Ramo Wooldridge Inc., Cleveland, Ohio, a corporation of Ghio Filed May 16, 1958, Ser. No. 735,768 Claims. (Cl. 323-22) This invention relates to electrical power supply circuits and more particularrly to a power supply circuit including at least one control element such as a semiconductor transducing device of the transistor variety which is controllably biased to maintain a substantially constant voltage across a pair of output terminals.

Where it is necessary to provide a substantially constant unidirectional voltage, it is well known to connect regulator devices between a source of primary supply voltage and a pair of output terminals. In some instances peak currents are drawn from a regulated power supply which are in excess of the average current rating of the regulator device itself. Such peak currents may arise due to the accidental short-circuiting of the output terminals of the power supply `as well as from the mal-functioning of a load circuit connected to the power supply terminals.

Where electron tubes are employed as regulator devices, an accidental short-circuiting of the power supply output terminals -generally does no permanent damage, since most electron tubes possess a relatively high internal im.- pedance which limits short-circuit or overload currents to reasonable and safe values, at least for time periods sufliciently long to permit conventional thermal fuse type protection. In addition, the maximum current flow in an electron tube is limited to the saturation current which is reached when the current includes all of the limited num- -ber of electrons made available by the cathode structure. On the other hand, controllable conductance semiconductor type transd'ucing devices, such as transistors, generally possess a very low internal impedance which does not inherently limit the current flow therethrough to safe values. Also, in present-day commercial power transistor devices, the current flow is by means of mobile charge carriers within a body of semiconductor material, and no inherent current limiting edect is present for current densities below that producing actual fracture or fault in the semiconductor device. However, the paramount consideration in the overload failure of known power transistors appears to be the power dissipation produced at the junctions within the transistor. The junction power dissipation characteristic of a transistor may be referred to as the iZt rating of the device is somewhat the same way as thermal fuses are rated where i equals the current llow and t equals time. The z'zt rating is dependent upon the heat transfer characteristic of the semi-conductor material itself, as well as the heat transfer characteristic of the junction materials and conductors connected thereto. Shortterm current overload in a given power transistor, for practical purposes may, therefore,` be thought of as occurring only when current overload of a predetermined value is is sustained therethrough for a period of time ts causing the quantity of i521*s to exceed a predetermined value which may be termed the fault value F (in ampereZseconds). The junction power dissipation characteristic, l`2z, is to be distinguished from the maximum long-term current or continuous duty rating IL of a given transistor device which is lbased upon maximum permissible continuous power ydissipation therein when the device is operating in thermally coupled relation to its surroundings which may include a heat sink of predetermined capacity. The permissible short time value of overload cur-rent s may therefore be several times larger than the continuous duty value of current IL, provided its `duration is sutliciently ice short. Thus in a regulated power supply utilizing a transistor device as a regulating means, either la short-term current llow for a given time duration productive of a value of i2t in excess of the value F or a long-term current flow in excess of IL may cause permanent damage to or completely destroy the transistor device in a time period too short to permit thermal fuse type protection.

It is common practice in electrical power supply circuits, and more particularly in `a transistorized series regulated power supply, to employ two or more transistors connected in parallel relation to one another to increase the value of maximum current which may be safely delivered by the power supply over that of the currenty rating of a single transistor. However, experience shows that it is in general quite difficult to cause two parallel connec-ted transistors to properly share current flow in ka given electrical circuit branch without connecting a lixed resistance in series with each transistor. ln regulated power supplies of the type being considered, in order to enforce proper load current sharing between two parallel connected regulating transistors, it has been found necessary to employ series connected resistances of relatively high value with the result that some of the desirable low impedance regulating characteristics of the transistor are lost. Also, where parallel connected transistors are employed, it is commonplace t-o lind that, in the course of use, the characteristics of one transistor may change, due to aging or the development of a fault. The result is that `a greater load may be imposed on some of the parallel connected transistor devices than on `others which, under certain conditons, may result in a ch'ain destruction of all of the parallel connected transistors.

Regardless of whether or not the series regulating transistor device of a transistorized regulated power supply comprises a single transistor or a plurality of parallel connected transistors, known forms of prior art regulating circuits provide no means for correcting output voltage changes attributable to variations in actual source potential upon which the transistor regulating device acts. That is, the source potential which the series regulating transistor controllably couples to the output terminals of the power supply may itself change due, to various causes either independently of or dependent upon the load current drawn from the power supply terminals.

The present invention, therefore, has as its main objective the provision of :an improved transistorized regulated power supply which embodies novel protective and control circuit arrangements operating to overcome the above problems associated with the use of transistors as voltage regulating devices. ln addition, the present invention utilizes a transistor as a series regulating device in a manner which affords regulation of an output voltage to compensate for changes in the value of a source voltage applied to the regulating device as well as changes in the value of current delivered to a load.

In accordance with one aspect of the present invention, a regulated power supply is provided in which -at least one regulating transistor is connected serially between one terminal of a two-terminal source of voltage and one of two power supply output terminals. The value of emitterbase bias current on the transistor is controlled as an inverse function of output voltage to maintain (by negative voltage feedback) the power supply output terminal potential substantially constant.

In order to protect the transistor from overload, in

the event of a short circuit across the output terminals, the present invention takes advantage of the inherent charge mobility characteristics of transistors. It isknown that charge carrier (electrons and holes) mobility in a semi-conductor material, especially as employed ina transistor device, is rappreciably less than electron mobility in a conductor or vacuum or gas, or the mobility of ions in an ionized 'gaseous atmosphere. yIt is further observed that transistors designed to operate at high current densities and to deliver high currents (such as power transistors) exhibit lower charge mobility than low current density transistor devices (such as high frequency amplifier transistors) Therefore, in accord-ance with the present invention, a fast-acting means is provided for responding to load current demands in excess of a predetermined maximum current value, to impose a negative current feedback on the regulating transistor. That is, as load current values in excess of a given value tend to increase, the negative current Ifeedback action acts to counteract this increase. The fast-acting negative current feedback means preferably comprises a transistor amplifier device having a greater charge mobility (or higher alpha cut-off frequency) than the series regulating transistor. Thus, upon ythe occasion `of ian overload or short circuit current, the negative current feedback circuit acts more quickly to reduce current ilow through the regulating transistor than the speed with which current can build up through the regulating transistor. In addition, the speed of the negative current feedback circuit is made sufficiently fast and of great enough range to limit the average v-alue and duration of overload current through the regulating transistor to values not exceeding the z'2t fault rating of the regulating transistor.

In further accordance with the present invention, the negative current feedback circuit is arranged to have a speed of response which is faster than the inherent speed of response of the negative voltage feedback (voltage regulating) circuit means. Thus, upon the occasion of overload or short circuit current conditions, the negative current feedback circuit reduces current flow through the regulating transistor faster than the negative feedback (voltage regulating) circuit can act to increase current iiow through the regulating transistor.

Still another laspect of the present invention resides in the provision of both a negative voltage responsive feedback circuit and a negative current responsive feedback circuit acting on a series regulating transistor device with threshold means incorporated in the negative current feedback circuit to prevent action thereof for power supply delivery currents less than a predetermined maximum, said -feedb-ack circuits being arranged to inter-act over a range of voltage values corresponding to a range of load impedances otherwise demanding currents in excess of s-aid maximum. Still another aspect of the present invention resides in the provision of a negative voltage regulating feedback circuit, in a transistorized power supply of the type abovementioned, in which the feedback circuit is made responsive to voltages appearing at both terminals of the regulating transistor.

vIn one particular embodiment of the invention, at least one regulating transistor is biased to compensate for both variations in the value of a voltage from a source and variations in the value of a voltage appearing across the output terminals, land a threshold means is actuated in accordance with increases in current flow beyond a predetermined value to bias the regulating transistor in a direction of minimum conductivity to limit the maximum current flow ltherethrough to a safe value.

In another alternative embodiment of the invention, a plurality of regulating transistors are connected in parallel with each other, a current sensing circuit sequentially renders each of the regulating transisors conductive to acconu-nodate increases in current iiow, the transistors are biased to maintain a const-ant output voltage, and a protective circuit biases the transistors in a direction of minimum conductivity in response to excessive current flow. Through `a sequential control action, predetermined ratios of current sharing between transistors can be reliably enforced without high values of series connected resistors.

A better understanding of the invention may be had `from a reading of the lfollowing detailed description and an inspection of the drawings, in which:

FIGURE l is a combined block and schematic circuit diagram of a regulated power supply in accordance with the invention including a protective circuit;

FIGURE 2 is a combined block and schematic circuit diagram of a regulated power supply in accordance with the invention illustrating an alternative arrangement of a protective circuit;

FIGURE 3 is `a combined block and schematic circuit diagram of a regulated power supply in accordance with the invention illustrating the manner in which parallel connected regulating transistors are afforded individual protection from overload;

FIGURE 4 is a schematic circuit diagram of -a preferred form of a regulated power supply employing the fundamentals of the present invention illustrated in FIGURE 1; and

FIGURE 5 .is a combined block and schematic circuit diagram of a regulated power supply in accordance with the invention, in which parallel connected regulating transistors are sequentially energized to increase the current capacity of the power supply when required.

FIGURE l illustrates a regulated power supply in accordance with the invention in which an yalternating current wave derived from a conventionai A.C. power source 1 is passed to a reetiiier means 2 via a transformer 3 to derive a unidirectional (D.C.) voltage from the alternating current wave. A filter capacitor 4 functions to remove alternating current components from the unidirectional voltage. Generally, the rectifier means 2 will possess a substantial amount of internal impedance, so that the rectified voltage appearing across the capacitor 4 varies with fiuctuations in Ithe amount of current ow drawn' by a load 5` from a pair of output terminals 6 and 7.

In order to provide a substantially constant regulated Voltage at the output terminals 6 and 7, a regulating transistor S i-s connected serially between the rectifier means 2 and the output terminal 6. The regulating transistor 8 may be one of many commercially available types having a `current and power handling characteristic adequate for supplying average load current demands for which the power supply is intended. In practice, the transitor 8 will be of the power transistor variety having a relatively low alpha `cutoff frequency attributable to limited charge carrier mobility within the transistor. rIfhus, the maximum speed with which current through the transistor 8 can be changed, by any means, is limited to a predetermined value. By way of example, the transistor 8 is shown to be of the N-P-N variety although the circuit may be readily modified to employ a transistor of the P-N-P type.

In operation, the -transistor 8 is controllably biased to, in turn, so control its conductance as to maintain 'a constant voltage between the output terminals 6 and 7 with a Variable portion of the volta-ge delivered by the rectilier means 2 appearing lbetween the collector and emitter of the transistor 8. In order to apply a control bias to the transistor 8` to regulate fthe voltage between the output terminals 6 and 7, a negative voltage feedback control circuit is employed. The negative feedback control circuit responds to a composite volta-'ge representing primarily -the variations in voltage appearing between the Output :terminals 6 and 7 and secondarily the variations in the voltage actually delivered to the transistor by the rectifier means 2 for regulation. A substantially fixed potential source 9' connected serially with a resistor 10 operates as a Voltage divider in which a constant volitage is subtracted from the output voltage by the fixed potential source 9 so that substantailly the entire amplitude of any fluctuations of the output voltage appearing across the resistor 10 is applied to an adder 11. In this particular form of the invention, a delay network comprising a resistor 12 and la capacitor 13 is interposed between the resistor and adder 11.

' In addition to the voltage appearing across the resistor 10, the adder `11 receives a portion of the voltage actually delivered to the transistor for regulation. This voltage is derived from the output of the rectifier means and applied to the adder via a variable resistor 14. Accordingly, the adder 11 produces a composite feedback control voltage primarily representing liuctuation-s in value of the voltage appearing between the terminals 6 and 7, and secondarily, liuctuations in voltage supplied by the rectifier means 2.

The composite feedback voltage from the adder 11 is applied to the base of a control transistor 15 which may be for example an N-P-N type. The emitter-collector output termials of the transistor 15 are connected between the base of the regulating transistor and the grounded negative output terminal 7. A resistor 16 is connected from the collector to the base of the regulating transistor l8 and applies a bias to the transistor base in a forward direction. The transistor 8 is therefore normally conducting so as to present a low impedance or high conductance between the rectiier means 2. and fthe output terminal 6. By virtue 0f the collector of the control transistor 15 being more positive than the emitter or base, it too will be rendered normally conducting. However, since the collector of the transistor 15 is lconnected to the base of the regulating transistor 8, a variation in collector current of the transistor 15 produces a variation in voltage drop across the resistor 16 which varies the potential appearing at the blase of the regulating transistor 8, hence controlling the base-emitter current to the transistor 8, which in turn varies the impedance or conductance appearing between collector and emitter of the regulating transistor 8.

Accordingly, if a drop occurs in the voltage appearing between the terminals 6 and 7, a drop in the value of potential appearing across the resistor 10 results and the control transistor 15 increases the base-emitter current of the transistor 8 which increases the collector-y emitter conductance thereof so as to reduce the voltage drop yappearing between the collector and the emitter. The reduction in voltage drop across the transistor 8 adjusts (increases) the potential between the termin-als 6 and 7 in a direction which tends to maintain the output voltage constant. On the other hand, any tendency for the voltage between the terminals 6 and 7 to increase, causes an increase in the Voltage appearing across the resistor 1b, an increased current flow through the transistor 15, a decrease in emitter-base bias current of the transistor 8, and a decrease in the collector to emitter conductance of the transistor The increase in voltage drop across the transistor 8 adjusts (decerases) the potential between the terminals 6 and 7 in a direction which tends to maintain a constant output voltage. Thus, a negative voltage feedback `circuit has been provided which regulates the volttage delivered to the terminals 6 and 7. In a similar fashion, any tendency on the part of the voltage delivered to the transistor for regulation (i.e., that voltage appearing between the collector of transistor 3 and circuit ground) to fluctuate, is also applied to the base of the control transistor 15 in such a way as to increase or decrease the bias applied to the regulating transistor S in a direction which tends to -maintain a constant output voltage across output terminals 6 and 7.

Although the regulated power supply of the invention will generally be employed to maintain ya constant value of voltage between the terminals 6 and '7, a particular lfeature of advantage of the arrangement of FiGUREl is that the proportional amount of lche voltage from the rectifier means 2 applied to the adder 11 may be adjusted by means of the variable resistor 14 Ito achieve other than a lconstant output voltage. By reducing the resistance value of the resistor 14, an increased amount of voltage from the rectifier means 2 may be applied to the adder 11 to produce an over compensation in the negative voltage feedback applied to the regulating transistor 8. By means of such over compensation, the voltage appearing between the terminals 6 and 7 may be made to rise with increased amounts of current flow drawn by the load 5. Thus, a rising voltage-current characteristic may be achieved which is desirable for some applications. On the other hand, an increase in the value of the resistance of the resistor 14 reduces the portion of the voltage from the rectifier means 2 applied to the adder 11 with the result that an under compensation in the negative voltage feedback applied to the regulating transistor 8 takes place. By means of under compensation, the voltage between the terminals 6 and 7 may be caused to decrease with increased current flow drawn from the terminals 6 and 7 by the load 5. Thus, a halling voltage-current characteristic may be achieved which is desirable for other applications.

While the portion of the power supply of FIGURE `1 thus far described functions satisfactorily over a wide range of variations in current being drawn from the terminals 6 and 7, it is well known, as described above, that transistors are subject to damage by short-term peak current dow therethrough, the duration (t) of which taken in combination with the value of current (i) drawn represents an 2t product in excess of a given critical it fault value F. Also, a transistor may be damaged by excessive long-term current dow, causing the power rating of the transistor to be exceeded. Accordingly, should the load 5 draw an excessive amount of current, or should the terminals K6 and 7 accidentally be short-circuited, the regula'ting transistor i8 may be damaged. The negative feedback voltage control effected by the transistor 15 increases the chance of such damage by attempting to maintain a constant voltage at the output terminals 6 and 7.

lIn order to protect the regulating transistor 8 from excessive values of current flow -which would otherwise damage the transistor `8, the power supply of FIGURE l, according to the present invention, includes a protective circuit means in the form of a negative current feedback path which regulates the current iiow through the regulating transistor y8 to a predetermined value less than the maximum permissible z2t value, F, as well as the lo-ngterm overload current I.

The protective circuit in FIGURE l includes an impedance in the form of a resistor 17 connected serially between the grounded output terminal 7 and the negative return to the rectifier means 2. Since all of the current passing through the regulating transistor y8 also passes through the resistor 17, a voltage appears across the resistor 17 which is indicative of the value of the current dow. A threshold means y18 is connected serially with a resistor 19 to sense the appearance of a voltage across the resistor 1'7 representing current flow of a predetermined safe maximum value.

The threshold means 118 may comprise one or more serially connected Zener diodes having a predetermined 1breakdown voltage at which the diodes become conducting so that a Voltage is applied to the emitter of a protective transistor 20.

When the threshold means conducts, a voltage appears across the resistor 19 and the emitter-base junction of the transistor 2t) is biased in a forward direction, thereby increasing the amount of current iiowing from its collector to its emitter. The increased `current iiow through the protective transistor 20 corresponds to a lower impedance 'between its collector and emitter, thereby effectively reducing the gain of the voltage feedback circuit based upon transistor 15. The base-emitter bias current of the regulating transistor 3 is thereby reduced. This decreases the conductance fbetween the collector and emitter of the regulating transistor `8 to limit the current iiow therethrough to a safe value.

As described above, the charge carrier mobility and alpha cutoff frequency in a power transistor are generally 7 Y lower than in the type of transistor employed for low power amplification. Accordingly, in the circuit of the invention, the protective circuit including the transistor 20, which may be of a low power type having a high charge carrier mobility and alpha cutoff frequency, is capable in its circuit environment, of rapidly responding to an overload current now indicated by the voltage across the resistor 17 so as to alter the bias current of the regulating transistor `8 in a direction which limits the current llow to a safe value before any damage to the regulating transistor occurs and before the control circuit including the resistor can function to increase the current ow through the regulating transistor 8. The speed with which the ycurrent protective circuit operates is made sucient to insure that even though the peak cunrent drawn lat any instant may exceed the continuous duty current rating of the transistor, the Iduration of such peak current is sulicient-ly short to prevent damage to the transistor.

In addition, since the regulating transistor `ta need not be completely cut olf, the circuit of the invention is capable of supplying a regulated current to the terminals 6 and 7 of a value which will not damage the transistor 8. Accordingly, over a -rst range of current values the circuit supplies a regulated Voltage at the terminals 6 and 7 under the sole iniluence of the control circuit including the transistor 15, over an intermediate range of current values the control circuit and protective circuit may operate jointly to control power delivery to the terminals 6 and 7, and over a high range of current values the protective circuit employing transistor over-rides the control circuit of the transistor 1S so that the power supply becomes essentially a current regulated device.

A substantial advantage over prior devices is accomplished by the circuit of the invention in that during periods of peak current tlow, the protective circuit limits the current dow to a safe value, but upon a reduction in v the current drawn from the terminals 6 and 7, the protective circuit ceases operation and the circuit is capable of supplying a regulated voltage at the terminals 6 and 7 'without resetting any protective device such as the -type ordinarily employed in which the protective device once actuated must be manually reset to restore the normal regulating operation.

As noted above, the protective circuit of FIGURE l has an inherent ability to respond rapid-ly to an increase in current flow through the regulating transistor 8 caused by the action of the control circuit in attempting to maintain the voltage at the output terminals 6 and 7 constant. However, the prior operation of the protective circuit in disabling the regulating operation may be assured by the inclusion of a time delay network comprising the resistor 12 and capacitor 13 which slightly retards the application of the voltage appearing across the resistor 10 to the base of the transistor 15. Thus, in the event of a short circuit or overload current, the action of the protective circuit in lowering the base-emitter 4bias current lof the regulating transistor Si occurs prior to the decrease in current Eflow through the control transistor 15 which would otherwise tend to increase the base-emitter bias current of the regulating transistor 8.

An additional feature of the circuit of FIGURE l is the inclusion of a capacitor 21 across the output terminals 6 and 7. In addition to functioning as a lter for any unwanted alternating current components, the capacitor 21 enhances the operation -of the protective circuit in supplying a portion of the current flow from the terminals 6 and 7 when a short circuit or overload current condition occurs. Thus, the current demand on the regulating transistor 8 increases only as the capacitor 21 discharges, which reduces the rate of increase of current flow through the regulating transistor 8` so that the protective circuit has additional time in which to alter the base-emitter bias current of the transistor 8 to limit the current flow therethrough to a safe'value without the z'2t rating of the transistor being exceeded.

An alternative arrangement of a regulated power supply in accordance with the invention is illustrated in FIG- URE 2 in which a protective circuit is connected serially with the ibase of a control transistor 23 to reduce the etiective gain of the negative voltage feedback circuit and limit the current flow through a regulating transistor 24 to a saife value under short circuit current conditions. As in FIGURE l, a negative feedback control voltage representing iluctuations in the output Voltage appearing at the output terminals 25 and 26 may be derived from a resistor 27 and a fixed potential source 28 for application to the base of the control transistor 23 Via a protective transistor Z9 which may be a P-N-P type. Although omitted in FIGURE 2, it will be appreciated that a composite negative feedback voltage may be employed representing both the voltage from the rectiiier source 30 as well as the voltage between the output terminals 25 and 26 as described above in `connection with FIGURE l.

In operation, when the voltage appearing across the resistor 27 reflects a change in the output voltage, the current flow through the transistor 23 increases or decreases to vary the base-emitter bias current of the regulat-ing transistor 24 in a direction which tends to regulate the voltage of the terminals 2S and 2'6. In the event of a short circuit 0r overload current, a voltage appears across a resistor 31 which renders the Zener diode threshold device 32 conductive to pass a current through a resistor 33. The resulting voltage across the resistor 33 increases the emitter-base bias current through the protective transistor 29, which Iin turn increases the baseemitter bias current through the control transistor 23, and lowers the potential -on the base of the regulating transistor 24 due to the increased current ow through a base current feed resistor 34. Accordingly, the current flow between the collector and emitter of the transistor 241 is limited to a safe level by negative current lfeedback.

The regulating transistor 24 will generally comprise a power transistor having a low alpha cutoii' frequency while the protective and control transistors 29 and 23 will generally comprise ordinary transistors having a higher alpha cutoff frequency. Accordingly, the protective circuit of FIGURE 2 possesses the same inherent ability to respond to a short circuit or overload current condition as that of FIGURE 1, due to the diierence `in charge carrier mobility between the regulating transistor 24 and the protective and control transistors 29 and 123. In addition, a capacitor 35 across the output terminals Z5 and 26 supplies current under short-term overload or short circuit conditions as described above in connection with FIGURE 1.

In FIGURE 3 there is illustrated another alternative embodiment of the invention in which the current capacity of the power .supply is increased by connecting a pair of N-P-N type regulating transistors 36 and 37 in parallel between a source of power comprising a rectier means 3S and one of a set of load accepting output terminals 39 and di). Each of the transistors 36 and 37 presents three operating terminals respectively connected to the emitter, base and collector of each. Thus each transistor comprises one form of semiconductor transducing device presenting one pair of input terminals (e.g., corresponding to the collector and emitter) and one pair of output terminals (e.g., corresponding to the base and emitter). In the embodiment shown in FIGURE 3, the output terminals of each device are connected in parallel with one another leaving the input terminals available -for separate or joint control. Negative voltage deed-back for regulating the voltage appearing across the terminals 39 and 40 is then provided in the circuit of FIGURE 3 from a single control transistor 41 which receives a voltage lfrom a resistor 42 connected serially with a Zener diode 43 which functions as a fixed potential source. The control transistor 411 responds to variations in .the voltage across the resistor 42 to pass a current which controllably biases,

on a joint basis, both of the regulating transistors 36 and 37 to maintain a substantially constant voltage between the output terminals 39 and 40. A common bias current feed resistor 44 may be connected between the rectier means 38 and the transistors 36 and 37.

According to the form of the invention shown in the arrangement of `FIGURE 3, separate current sensing resistors 45 and I46 are connected serially with each of the regulating transistors 36 and 37. Should the voltage appearingl across either the resistor 46 or the resistor 45 indicate that an excessive amount of current is flowing through its corresponding transistor, one -or both of the Zener diodes `47 and 48 is rendered conducting, thereby completing a circuit in which emitter-base bias current flows through a P-'N-P transistor 49. Transistor 49 normally is in a low conductance condition or in fact cut off. A resistor 74 may be connected between the emitter of the transistor 49 and ground reference potential. In the presence of emitter-ibase bias current through the transistor 49, the transistor exhibits lowered impedance across its output terminals and a Zener diode 50 receives an increase in the potential from the collector of the transistor `49 which renders it more conducting and increases the voltage appearing across a resistor 51.

Still considering the condition of current overload in either or lboth transistors 36 or 37 in FIGURE 3, the voltage across the resistor 51 is sucient to render another Zener diode 52 conducting to produce -a voltage across a resistor 53 which is applied to the base of a protective transistor 54. In turn, the voltage Ifrom the resistor 53 increases the base-emitter bias current of the protective transistor 54. This in turn increases the conductance of the transistor 54 and increases the voltage drop across resistor 44 to reduce the base-emitter bias current .of the regulating transistors 36 and 37 which limits the current flow therethrough to a safe value. Again the action of transistor 54 may be thought of as reducing the gain of the negative voltage Ifeedback circuit by shunting the output of transistor `4l in the event of current' overload. As before, where the regulating transistors 36 and 37 are selected to have a lower alpha cutoif frequency than the .control and protective circuit transistors 4l, 49, and 54, the protective circuit is inherently fast acting. However, a capacitor 55 connected across the output terminals 39 and 46 affords additional protect-ion as described above and, if required, a time delay circuit may be included in the control circuit as illustrated in FIGURE l. l

The circuit of FIGURE 4 illustrates a preferred way of carrying out the principles described above in connection with FIGURE 1. The circuit of FIGURE 4 includes a bridge rectifier 56 which provides a unidirectional voltage across a filter capacitor '7. Between the bridge rectier 56 and one of the output terminals 58 and 59, a regulating transistor 6ft is connected. A negative voltage control :feedback circuit is included in which a Zener diode 61 and a pair of adder resistors y62. and 63 sample the Kiluctuations in voltage at the output terminals 58. and 59. In addition, a portion of the voltage from the rectitier means is supplied to the resistor 63 via a resistor '64 so that a -composite negative feedback voltage is applied'to the 'base of a control transistor 65.

In the arrangement of FIGURE 4, an amplifying transistor 66 is connected serially with a current limiting resistor 67 between the control transistor `65 and the regulating transistor 60 to amplify the negative feedback signals whereby more gain is afforded in the voltage regulating negative feedback loop and a more effective and positive control may be exercised over the regulating transistor 60 which may require relatively wide swings in base-emitter bias current for effective control.

A bias current feed resistor 73 may be connected between the collector of transistor 60 and base of the amplifying transistor 66 so that the voltage applied to the base of the amplifying transistor 66 varies with current ow through Ithe control transistor 65 and with variations in the voltages appearing across the resistors 62 and 63. In turn, the amplifying transistor `66 varies the baseemitter bias current of the regulating transistor 60 t0 maintain a constant voltage at the output terminals 58 and 59.

The protective circuit of FIGURE 4 includes a current sensing resistor 68 in the ground return lead to the bridge rectifier 56 which renders a Zener diode 69 conducting in response to current flow therethrough in excess of a predetermined safe current value. The Zener diode 69 passes a current through a resistor 70 and the voltage appearing across the resistor 70 is applied to the emitter of a protective transistor 71.

In response to a voltage'across the resistor 70, the baseemitter bias current of the protective transistor 71 is increased, thereby increasing the current ow therethrough which decreases the base-emitter bias current of the amplifying transistor 66, which in turn decreases the baseernitter bias current of the regulating transistor to limit the current flow therethrough to a safe value. As before, Ithe regulating transistor 66 will generally be of a type which has a low alpha cutoff frequency While the other transistors 66, 65 and '71 comprise .types having rela-tively high alpha cutoff frequencies so that the protective circuit is capable of functioning prior to the build-up of current in the regulating transistor 60. A time delay circuit like that shown at 12 and 13 in FIGURE l may be included in the control circuit if required to delay the application of the negative voltage feedback, and a capacitor 72 may be connected across the output terminals 5S and 59 for the same purpose as that described above for capacitor 55 in FIGURE 3.

FIGURE 5 illustrates a regulating system for a power supply in accordance with the invention in which the number of parallel connected regulating transistors may be sequentially increased when required to increase the over-all current capacity of the regulating system. Accordingly, in FIGURE 5 two current regulating transistors 75 and 76 are connected in parallel paths between a rectifier 77 and one of the output terminals 7 8 and '79. The circuit is arranged so that the upper conductive path includ-ing the regulating transistor 76 is operated continuously and the lower conductive path including the transistor 75 is enabled to pass current when `the current flow in the upper conductive path rises above a predetermined level.

In a fashion similar to that described previously, the base-emitter bias current of each of Ithe transistors '75 and 76 is varied to sustain a substantially constant voltage across the terminals 78and 79. A negative feedback voltage is derived by means of a Zener diode S0 and a resistor 81 connected serially which is applied to two control transistors 82 and 53. The control transistors 82 and 83 serve to vary the base-ernitter bias current of each of the regulating transistors 75 and 76 in a manner substantially the same as that described above in connection with the embodiment or" the present invention shown in FIGURES 1 and 2. A pair of base current feed resistors 84 and 85 may be connected between the rectier 77 and the transistors 75 and 76.

`For low values of current flow through the upper path including the regulating transistor 76, the lower path including the transistor 75 is disabled due to the flow of current through a protective transistor 87 to which is applied a Vfixed bias from a source of potential such as a battery 86. The battery 86 maintains the protective transistor 87 normally conductive so that the base-emitter bias current of the regulating'transistor 75 is held 'at a low level and a low conductance is presented to current flow in the lower circuit path by the regulating transistor 75. Accordingly, for relatively low values of current ilow, substantially all of the current ilows through the upper circuit path and the regulating transistor 76 with4 aplicar the control transistor 83 varying the base-emitter bias current of the regulating transistor 76 to sustain a substantially constant voltage across the output terminals 78 'and 79.

Current ilow through the upper circuit path produces a voltage across a potentiometer 89 which is applied to the base of a transistor 90 via a fixed resistor 91. The emitter of the transistor 99 may be returned to ground reference potential via a resistor 92. A11 increase in applied voltage to the transistor 90 increases the voltage across a voltage divider comprising a Zener diode 93 and a resistor 94. As the `amount of current drawn through the upper circuit path increases, the Zener diode 93 is rendered conducting and the voltage across .the resistor 94 increases. At a predetermined level a threshold device in the form of a Zener diode 95 is rendered conducting to produce a voltage across a resistor 96. The voltage appearing across the resistor 96 over-rides the potential of the battery 86, thereby applying a bias to the emitter which renders the transistor 87 less conducting. When the transistor '57 is rendered sutliciently less conducting the base-emitter bias current of :the lower circuit path regulating transistor 75 increases to enable the lower conductive path to pass current between the rectilier 77 and the output terminal 78. Accordingly, in response to an increase in current ow in the upper circuit path beyond a predetermined level, the lower circuit path is rendered 4operative to increase the current capacity of the power supply.

Although only two sequentially operated circuit paths have been illustrated in FIGURE 5, it will be appreciated that any number of additional circuit paths may be included which are either operated continuously in parallel as in FIGURE 3, or sequentially rendered conductive as in FIGURE 5.

In order to protect Ithe regulating transistors 75 and 76 from excessive amounts of current flow, a voltage may be derived representing the current iiow through each of the current paths. As described above, a voltage is applied to the base of the transistor 90l from a potentiometer 89 via a resistor 91 representing the value of the current flow in the upper circuit path. ln a similar fashion, a potentiometer 97 may be connected serially in the lower circuit path with a voltage being applied to the transistor 90 via a resistor 98. Thus, when both of the circuit paths are rendered operative, a potential is applied to the base of the transistor 9i) representing the current flow in each of the circuit paths. Accordingly, an amount of current flows through the transistor 9@ in accordance with the current ilow in each circuit path and a corresponding voltage appears across the voltage divider of the Zener diode 93 and resistor 94.

By a suitable selection of a threshold device in the form of a Zener diode 99, a negative current feedback voltage may be produced across a resistor '100 whenever the voltage across the resistor 94 rises to a predetermined level indicating a maximum safe value of current ilow in each of the circuit paths. The Zener diode 99 should be arranged to have a higher threshold value at which it conducts than the Zener diode 95 which conducts to render operative the second circuit path. Whenever a voltage appears across the resistor 110i), the protective transistor 87 and a protective transistor 88 are biased to a state of conduction which decreases the base-emitter bias current of both of the regulating transistors 7S and 76 which limits the current flow therethrough to a safe value.

As before, by a selection of the regulating transistors 75 and 76 to have a lower alpha cutoff frequency than the control and protective transistors `82, y83, 87, 88 and 90, the protective circuit is inherently lfast acting. A capacitor 101 connected across the output terminals 78 and 79 works as described above to reduce the rate of current increase through the regulating transistors 75 and 75 upon a sudden increase in current drawn from the output terminals 78 and 79. In addition, la delay circuit may be included in the negative voltage feedback path of the control transistors 8,2 and `$3 if desired to lretard the current build-up in the regulating transistors S2 and 33 to insure a limitation of the current flow through the regulating transistors and 7 6 by the negative current feedback circuit including the protective transistors 37 and 88 under overload or short circuit conditions.

Although various alternative arrangements of the invention have been illustrated in FIGURES 1-5, it will be appreciated that the illustrative circuits are intended to be by way of example only. Accordingly, various combinations ofthe features shown in each of the circuits, or modiiications thereof which infact constitute clear equivalents, should be considered to be Within the scope of the invention. rln addition, throughout Ithe several figures the threshold means and fixed potential sources have been illustrated for convenience as a single Zener diode. Other fixed potential sources and threshold devices may be employed as well and where required a number of such devices may be connected serially to achieve a desired value of fixed potential or threshold of actuation.

Having thus `described the invention, what is claimed is:

1. A regulated power supply including the combination of: a source of unidirectional voltage; a pair of output terminals; at least one transistor connected serially between the source of unidirectional Voltage and one of the output terminals; a :control circuit coupled to the transistor for biasing the transistor to maintain a substantially constant unidirectional voltage `across the output terminals; means for sensing the value of the current drawn from the output terminals; and a protective circuit connected to the sensing means and operative upon said control circuit to limit the maximum current ilow through the transistor in response to current being drawn from the output terminals in excess of a predetermined value.

2. A regulated power supply including the combination :of: a pair of output terminals; a source of unidirectional voltage; at least one transistor connected serially between the source of unidirectional voltage and one of the output terminals; means biasing the transistor to control current therethrough in response to fluctuations in voltage appearing across the output terminals in a direction tending toI minimize variations in voltage at the output terminals; an impedance connected serially between the unidirectional voltage source `and one of the output terminals; and means coupled between the impedance and said biasing means for limiting the maximum current flow through the transistor in response to a voltage `across the impedance in excess of a predetermined value.

3. A regulated power supply including the combination of: a source of unidirectional voltage; a pair of output terminals; at least one regulating transistor having a base, a collector and an emitter, said regulating transistor collector and emitter being connected serially between the unidirectional voltage source and one of the output terminals; means `for deriving a composite voltage representing -both lfluctuations in the value of the voltage provided by the unidirectional voltage source and the value of the voltage `appearing across the output terminals; negative voltage feedback means coupled between the regulating transistor base and the composite voltage deriving means for regulating the voltage across the output terminals; an impedance connected serially between the source of unidirectional voltage and one of the output terminals; and negative current feedback means coupled between the impedance and the regulating transistor base for restricting the current flow through the regulating transistor to a predetermined maximum level in response to a voltage in excess of :a predetermined value yappearing across the impedance.

4. ln a voltage regulated power supply having a pair of output terminals to which load current demanding means are to be conditionally connected, it being desired that the value of Voltage across said output terminals remain substantially constant over a given range of load current demand values, the combination of a source of power :supply potential having a first pair of output terminals between which is developed a power supply voltage, said source exhibiting relatively poor voltage regulation characteristics across said first terminals as a function of current delivered by said source; a second pair of output terminals corresponding to the output terminals of the voltage regulated power supply; means establishing a condu-ctive path vfrom one terminal of said source to one of said second output terminals; means including a transistor connected between the other terminal of said source and the other one of said second out-put terminals; means responsive to the voltage appearing across said second ouput terminals to control the conductivity of said transistor in -a negative voltage feedback sense to reduce variations in voltage tending to appear across said second output terminals; means responsive to current delivered by said source to said second output terminals to control the .conductivity of -said transistor in -a negative current feedback sense, to reduce changes in load current delivered to said second terminals; and threshold means included in the negative current feedback circuit for withholding action thereof for currents less than a predetermined maximum value, whereby the voltage appearing across said second output terminals remains substantially constan-t over a given range of curnent the maximum value of which corresponds to said predetermined value and is substantially linearly reduced for currents in excess of said maximum.

5. A control circuit arrangement suitable for use in regula-ting the voltage and current lapplied to a set of load accepting output terminals from a source of electrical power, comprising in combination: tti-rst means defining a set of input terminals designated to accept power from a source of electrical power; second means defining a set of output terminals designated for power delivering con* nection to a variety of power demanding load means; coupling means including a controllable conductance semiconductor transducing device connected between said iirst and second means for establishing a controllable conyductance coupling path through said device `for current flow `from said input terminals to said output terminals; iirst control means operatively coupled to said device and said output terminals land responsive to the electrical potential conditionally appearing across said output terminals tor controlling the conducta-nce of said device as an inverse function of the value of potential appearing across said output terminals; second control means operatively coupled to said device, and serially connected between said input terminals and said output terminals and responsive to current ilow between said input terminals and said output terminals for controlling the conductance of said device -as an inverse function of the value of current ii-owy between said input terminals and said output terminals; and means operatively included in said second control means for establishing an operating threshold therein for withholding operation of said second control means' for all values of current ilow between said input and said output terminals which are below a predetermined threshold value.

6. A control circuit arrangement suitable for use in regulating the voltage and current applied to a set of load accepting output terminals from a source of electrical power, comprising in combination: iirst means deiining a set of input terminals designated to :accept power from ia source of electrical power; second means defining a set ld'- appearing across said output terminals 'for controlling the conductance of said device as an inverse function ot the value of potential appearing across said output terminals, said tir-st control means including means limiting the response speed thereof, whereby the speed with which conductance control of vsaid transducing device is eiiected inv response to the potential appearing across said output terminals is limited to a predetermined value; second control means operatively coupled to said device 'and serially connected between said input terminals and said output terminals responsive :to current flow between said input terminals and said output terminals for controlling the conductance of said device as an inverse function of the value of current iiow between said input terminals and said output terminals, said second control means includv ing means defining a speed of control response therein which is greater than the speed of response of sai-d tiret control means; land means operatively connected in said second control means for establishing an operating threshold therein for withholding operation of said second control means for all values of current llow between said input and output terminals which are bel-ow said current value l.

7. A control cir-cuit arrangement suitable for use in regulating the supply of power to a set of load accepting output terminals from a source of electrical power, comprising in combination: first means deiining a set of input terminals designated -to accept power from a source of electrical power; second means defining a set of output terminals designated tor power delivering connection to a variety of power demanding load means; coupling means including ya plurality of semiconductor transducing devices connected in parallel current sharing relation to one another between said first land second means for estraiblishing a plurality of separate controllable conductance coupling path-s through said devices Ifor sharing current flow `from said input terminals to said output terminals; means for selectively controlling the conductance of each of said devices independently of one another; and means operatively coupled .to said conductance controlling means :and serially connected between said input terminals and said output terminals responsive to current iiow between said input terminals and said output terminals for selectively control-ling the conductances of said devices as a function of lthe value of current il-ow between said input terminals and said output terminals so that load currents of higher magnitude are shared by more than one of said devices while load currents of lower magnitude `are shared by fewer of said devices.

8. A cont-rol circuit .arrangement suitable :for use in regulating the vol-tage and current `applied to a set of load accepting output terminals from a source of electrical power, 'comprising in combination: tirst means deining a set of input terminals, designated to accept power from a source of electrical power; second means `defining la set of output terminals designated vfor power delivering connection to a variety of power demanding load means; a plurality of controllable conductance semiconductor transducing `devices connected in parallel relation to one another to tonni Ia controllable conductance coupling means; means connecting said controllable conductance coupling means between said iirst :and second means for establishing a controllable conductance coupling path for current iiow ifrom said input terminals to said output terminals; `control means operatively coupled with each of said transducing devices for controlling the conductance of said devices on `a selective basis; and means connected between said input terminals, said output terminals and said control means, and responsive to current ilow between said input terminals an-d output terminals for maintaining the value of conduct-ance sustained by a first one of said devices relatively high with respect :to a second one of said devices for current iioW values below a iirst given value, increasing the conductance of said second one of said devices relative to said iirst one of said devices aoeaara for current flow values above said iirst given value but below a second higher given value, and decreasing the conductance of all of said devices tor current iow values in excess of said second given value.

9. A regulated power supply for maintaining a substantially cons-tant voltage across a pair of output terminals including the combination of a plurality of regulating transistors connected in parallel with each other and serially with one of the output terminals; means 'for fre-ndering `the transistors conductive one after another in response to increases in current drawn trom` the output terminals; means for controlling the internal impedance of each of the regulating transistors Ito sustain a substantially constant voltage across the output terminals; and means for limiting the maximum current flow through the transistors in response to current being drawn trom the output terminals in excess of a predetermined value.

10. A regu-lated power supply including the combination of a source of unregulated unidirectional voltage, a pair of output terminals, at least one regulating transistor connected serially between the unidirectional voltage source and the output terminals vfor regulating the voltage at the output terminals, said regulating transistor having a predetermined Aalpha cutoff frequency, a control transistor, a negative voltage feedback circuit including the control transistor connected between the output terminals and the regulating transistor for variably biasing the regulating transistor in response to uctuations in voltage appearing lat the output terminals; means for sensing current flow through the regulating transistor, a protective transistor having an 4alpha cutoff frequency higher than the alpha cutoff frequency of the regulating transistor, and a negative current feedback circuit including the protective transistor connected between the current sensing means and the regulating transistor for restraining the current ow through the regulating transistor at a value less than a predetermined value.

l1. A regulated power supply including the combination of -a source orf unidirectional voltage; a pair of output terminals; at least one regulating transistor having a base, `a collector and an emitter, said regulating transistor collector and emitter being connected serially between the unidirectional voltage source and one of the output terminals; an adder coupled to the output terminals and to the unidirectional Voltage source for deriving a composite voltage representing both fluctuations in the value of the voltage provided by the unidirectional voltage source and the value of a voltage appearing across the output terminals; means coupled to the adder for Varying the relative magnitudes of the voltage from the unidirectional source and the voltage from the output terminals appearing in the composite voltage; a negative voltage feedback means coupled between the regulating transistor base and the adder for regulating the voltage across the output terminals with variations in current drawn therefrom in accordance with a voltage current characteristic `determined by the relative proportions of the output voltage Iand the voltage from the source contained in the composite voltage from the adder; an impedance connected serially bctween the source of unidirectional voltage and one of the output terminals; and a negative cur-rent feedback means coupled between the impedance and the regulating transistor base tfor restricting the current flow through the regulating transistor to a predetermined maximum level in lresponse to a voltage in excess of a predetermined value appearing across the impedance.

12. In an electrical power supply circuit, the combination of a plurality of semiconductor transducing devices of the type exemplified by the transistor, each having an input pair of terminals and an output pair of terminals, the conductance appearing across the output terminals of a given device being a function of the signal conditionally applied to the corresponding input signal terminals of the given device; means connecting the output terminals of said devices in parallel with one another to form a current conducting combination, said combination having a plurality of control terminals corresponding to the input terminals -ot said idevices to permit separate control of the conductance sustained by each device in said current conducting combination; means defining a pair of power accepting terminals to which a source of electrical power may be conditionally connected for delivering current to a load; means deiining a pair of load terminals for conditionally accepting an electrical load to which current is to be supplied by a source of electrical power conditionally connected to said power accepting terminals; means connecting said current conducting combination between said power accepting terminals and said load terminals for conditionally Vdelivering current through said current conducting combination to a load circuit conditionally connected to said load terminals; means connected between said power accepting terminals and said load terminals for developing a signal the magnitude of which varies with the magnitude of the current supplied to a load conditionally connected to said load terminals; means connected to at Vleast one of said control terminals for establishing the conductance of a iirst one of said devices at a higher value than the conductance of at least `a second one of said devices; and means coupled between said signal developing means and at least one other of said control terminals for increasing the conductance of at least said second one of said devices when current supplied to said load exceeds a predetermined value.

13. in an electrical power supply circuit, the combination of a plurality of semiconductor transducing devices of the .type exemplified by the transistor, each having an input pair of terminals and an output pair of terminals, the conductance appearing across the output terminals of a given device being a function of the signal conditionally applied to the corresponding input signal terminals of the given device; means connecting the output terminals of said devices in parallel with one another to form a current conducting combination, said combination having a plurality of control terminals corresponding to 'the input terminals of said `devices to permit separa-te control of the conductance sustained by each device in said current conducting combination; means defining a pair of power accepting terminals to which a source of electrical power may be conditionally connected for delivering current to a load; means defining a pair of load terminals for conditionally accepting an electrical load to which current is to be suppl-ied by a source of electrical power conditionally connected to said power accepting terminals; means connecting said current conducting combination `between said power accepting terminals and said load terminals for conditionally delivering current through said current conducting combination fto a load circuit conditionally connected to said load terminals; means connected between said power accepting terminals and said load terminals for ydeveloping a signal, said signal developing means including a Aseparate current responsive signal information developing means connected -in series with each `device in its connection with said other devices in forming said current conducting combination; means connected to at least one of said control terminals for establishing the conductance of a iirst one of said devices at a higher value than the conductance of at least a second one of said devices; means coupled between said signal developing means and at least one other of said control terminals for increasing the conductance of at least said second one of said devices when current supplied to said load exceeds a predetermined value; and means responsive to said signal information and coupled with all of said input terminals for jointly decreasing the conductance of all devices upon the occurrence of current ow through any one device which exceeds a predetermined assigned value @associated with each device.

14. In an electrical power supply circuit, the combination of a plurality of semiconductor transducing devices of the type exemplified by the transistor, each having an input pair of terminals and an output panof terminals, the conductance appearing across the output terminals of a given device 'being la function of the signal conditionally applied to the corresponding input terminals of the given device; means connecting the output terminals of said devices in parallel -with one another to form a current conducting combination, said combination having a plurality of control terminals corresponding to the input terminals of said devices to permit separate control of the conductance sustained by each device in said current conducting combination; means defining a pair of power accepting Iterminals to which a source of electrical power may be conditionally connected `for delivering current to a load; means defining a pair of loa-d terminals for conditionally accepting an electrical load to which current is to be supplied by a `source of electrical power conditionally connected to said power accepting terminals; means connecting said current conducting combination between said power accepting terminals and said load terminals for conditionally delivering current through said current conducting combination to a load circuit conditionally connected to said load terminals; a separate current responsive signal developing means connected in series with the output terminals of each -device in its connection with said other devices in forming said current conducting combination to develop separate signals each representing the magni-tude of current flow in a diierent device; means combining said separate signals into a single control signal; and means coupled with al1 of said input terminals and responsive to said single control signal for decreasing the conductance of all of said devices upon the current flow through any one device exceeding a predetermined value assigned to that one device.

l5. A regulated power supply including the combination of a source of unidirectional voltage; a pair of output terminals; at least one regulating transistor having a base, a collector and an emitter, said regulating transistor being of a type having a predetermined alpha cuto frequency corresponding to a given charge carrier mobility, said regulating transistor collector and emitter being connected serially between the unidirectional vol-tage source and one of the output terminals; 1an adder coupled to the output terminals and to the unidirectional voltage source for deriving a composite voltage representing both fluctuations in the value of the voltage provided by the unidirectional voltage source and the value of a voltage appearing across the output terminals; means coupled to the adder for varying the relative magnitudes of the voltage from the unidirectional source 4and the voltage from the output terminals appearing in the composite Voltage; a negative voltage feedback means coupled between the regulating transistor base and the adder for regulating the voltage across the output terminals with variati-ons in current drawn therefrom in accordance with a voltage current characteristic determined by the relative proportions of the output voltage and the voltage from the source contained in the composite voltage from the adder; an impedance connected serially between the source of unidirectional vol-'tage and one of the output terminals; and a negative current feedback means coupled between the impedance and the regulating transistor base for restricting the current flow through the regulating transistor to a Apredetermined maximum level in response to a voltage in excess of a predetermined value appearing across the impedance, said negative current feedback means including a protective transistor having an alpha cutoff frequency higher than the predetermined alpha cutoff frequency of the regulating transistor corresponding to a higher charge carrier mobility than the given charge carrier mobility of the regulating transistor whereby Athe negative current feedback means is capable of restricting current flow through the regulating transistor under conditions of overload current flow.

References Cited in the iile of this patent UNITED STATES PATENTS 2,693,568 Chase Nov. 2, 1954 2,697,811 yDeming Dec. 2l, 1954 2,767,330 Marshall Oct. 16, 1956 2,809,301 Short Oct. 8, 1957 2,825,023 Marantette Feb. 25, 1958 2,888,633 Carter May 26, 1959 2,904,742 Chase Sept. 15, 1959 2,915,693 Harrison Dec. 1, 1959 

1. A REGULATED POWER SUPPLY INCLUDING THE COMBINATION OF: A SOURCE OF UNIDIRECTIONAL VOLTAGE; A PAIR OF OUTPUT TERMINAL; AT LEAST ONE TRANSISTOR CONNECTED SERIALLY BETWEEN THE SOURCE OF UNIDIRECTIONAL VOLTAGE AND ONE OF THE OUTPUT TERMINALS; A CONTROL CIRCUIT COUPLED TO THE TRANSISTOR FOR BIASING THE TRANSISTOR TO MAINTAIN A SUBSTANTIALLY CONSTANT UNIDIRECTIONAL VOLTAGE ACROSS THE OUTPUT TERMINALS; MEANS FOR SENSING THE VALUE OF THE CURRENT DRAWN FROM THE OUTPUT TERMINALS; AND A PROTECTIVE CIRCUIT CONNECTED TO THE SENSING MEANS AND OPERATIVE UPON SAID CONTROL CIRCUIT TO LIMIT THE MAXIMUM CURRENT FLOW THROUGH THR TRANSISTOR IN RESPONSE TO CURRENT BEING DRAWN FROM THE OUTPUT TERMINALS IN EXCESS OF A PREDETERMINED VALUE. 